The invention relates to an oil ring assembly for control of lubricating oil in internal combustion engines and reciprocating compressors.
In general, a piston ring device for use in an internal combustion engine comprises a compression ring assembly composed of at plurality of compression rings for gas-seal of a clearance between a cylinder and a piston and an oil ring assembly consisting of an oil ring fitted in an oil ring groove below the lower compression ring and drain holes extending from the side periphery to the inside of the piston. The oil ring assembly is utilized to form lubricating oil film between the compression ring and the cylinder and collect oil therefrom to a crank case.
The oil ring is less affected by combustion pressure but more influenced by the inertia force due to it own mass, as compared with the compression ring. Although gas pressure exerts no serious action to the back of the oil ring, the pressure acting on the front of the oil ring is important for formation of lubricating oil film. The known oil ring is provided with two upper and lower cylinder contacting faces and an expander, such as a coil spring, for expanding the oil ring radially to the cylinder with a high pressure to obtain a good oil-scraping effect.
One type of the known oil rings is integrally formed with two upper and lower cylinder contacting faces and a drain window therebetween to perform a so-called check-valve action. The oil ring is seated on the lower side of the oil ring groove during the upward stroke of piston and on the upper side of the oil ring groove during the downward stroke of piston to scrape out oil into the drain hole in the piston. The upper and lower cylinder contacting faces are expected to obtain a double oil-scraping effect.
However, the two upper and lower cylinder contacting faces make the oil ring taller and more massive, so that, in high speed operations, the oil ring performs an insufficient check-valve action and brings increasement in oil consumption. Furthermore, the face is relatively wide to need a high cylinder contacting pressure for formation of an appropriate oil film. This leads to increase in friction loss. Besides, the known axially large oil ring makes the piston or engine taller, heavier and more fuel-consumptive.
The other known type is usually employed in a gasoline engine. It is composed of two independent rails of copper and a spacer expander for urging the rails into close contact with the cylinder wall. It is radially flexible and well followable to the cylinder wall. The rails make the oil ring groove airtight to prevent it from scraping up oil. However, the oil ring is impossible to shorten the axial height to the extent that friction loss is reduced. Besides, it is not easy to be set in the oil ring groove.
In brief, the most important problem in the known oil ring is a relatively large consumption of lubricating oil in high speed operations in which the oil ring is less followable to the cylinder. Another problem is that the known oil ring is impossible to decrease friction loss. A further problem is that the know oil ring is too taller to lighten the engine.
For the purpose of solving the problems as described above, Japanese Patent Publication Sho No. 47-19650 discloses an oil ring with two thin rails. Japanese Utility Model Application Publication Sho 55-41502 discloses another oil ring with a single rail. However, the oil ring as disclosed has disadvantages one of which is that the expander prevents axial movement or check valve action of the rail. Another disadvantage is that the thin rail is distorted by the cylinder contacting pressure in the dish-like form to fail in sealing the oil ring groove.